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Old 10-24-2018, 07:23 PM   #121
popgun pete
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Re: Trigger Mechanism Design Rules

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Originally Posted by Rob Allen View Post
Agreed. Years ago, the most common handle in South Africa was the old Champion Cavallaro handle. The original ones only accepted a spear with a longer tail section (behind the spear notch) this caused problems when the spear pushed up against the roof of the sear box as it could affect the way it lay if the spear was not machined straight (commonly they were not straight). This was especially the case with older ones where the roof would wear. They halved the length of the tail section and this reduced that potential load flexing a lot. All Euro spears are now at the same measurement. I’m not sure who started to keep measurements uniform in Europe.
There was a move to a "universal gachete" or universal trigger in terms of the sear tooth shape and I have seen this term inscribed on the housing of a few "second stringer" European spearguns as distinct from the mainstream Cavalero and Beuchat spearguns. The rationale would be that a gun was then not restricted to its original spear and for a time it seemed that there was a "universal shaft" to fit these guns (in the same diameter shaft) and it was very much like the Cavalero shaft with a flat tail and a wedge shaped tail notch. My recollection is that these guns usually had a rear plastic grip handle, a plastic trigger and that often the dipping sear tooth design was employed where the spear tail on insertion into the sear box pushed the tooth down and then springs pushed the tooth back up to engage the spear tail notch when it slid into the correct position. The plastic grip handles were clamshell moldings and the overall construction was very light and some would say flimsy. These guns, I recall one brand was "Crawl", seem to have disappeared as well as the term "universal gachete" from the speargun world.

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Old 10-25-2018, 09:48 PM   #122
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Re: Trigger Mechanism Design Rules

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Probably a genius...
Yes a genius, Marc Valentin
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Old 10-26-2018, 03:32 AM   #123
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Re: Trigger Mechanism Design Rules

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About a year ago we changed our spear sear notch to a more square shape after doing destruction testing on our handle using different shaped notches. The "more square" notch increased the mechanism "hold ability" on average by around 40kg.

That is interesting … I would have thought that a C shape would be stronger than a square cut because there are no sharp corners that can propagate a weakness. I did some stress analysis testing on a computer and I always found that the weakest point in the sear shaft is the area between the shaft sear pin and the shaft sear and not the notch itself. Obviously it would be different from mech to mech as they have different measurements and different angles of attack with regards to how the spear shaft sits on the notch. In the test study, I was able to dramatically improve the stress analysis data by simply adding a bigger fillet on the right angle between the shaft sear back stop and the shaft sear. You can get away with a 2mm fillet and maybe even a 2.5mm fillet before touching the spearshaft back end. That little tiny change dramatically increased the strength of the shaft sear.
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Old 10-26-2018, 03:49 AM   #124
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Re: Trigger Mechanism Design Rules

Hi Spearq8,

When overpowered to destruction, the part that destructs is not the shaft. I agree, a square will have sharp edges and be weaker than a C shaped, but the fail is not the shaft. The sear in the mechanism itself distorts and or, bends the sear pivot pin. Our "square" sear notch in the spear does have rounded corners. The degree of glass content in the glass filled nylon cassette also plays a huge part in the mechanisms "hold-ability" as does the corners in the roof.
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Old 10-26-2018, 08:17 PM   #125
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Re: Trigger Mechanism Design Rules

The squarer shaft tail notch probably engages lower on the tooth. If you looked at a fully loaded up spear tail and sear tooth of the square cut type you would see that they would connect low on the tooth as the sear lever under extreme pressure tilts forwards slightly (1/4” sear lever pivot pin). Bill Kitto found that when he applied thousands of pounds of spear pull the slightly tilted tooth was torn off the sear lever by the spear tail which cut through the tooth, however these are not spearfishing loads and are for test purposes only. One way to lift the point of destruction higher was to square the flat faces up to each other so that the force is evenly spread which in turn meant that an over pushed sear lever for mechanism relatching could not be tolerated, over pushing being used in the heavy duty M3 Mechanism. Kitto developed the M5 two-stage locking derivative of the M3 for this very purpose, however anyone wishing to push these “MBT” trigger mechanisms to their limits will be handling a gun with scary band loads. One spearfishing identity, whom I will not name, put aside his vastly overpowered M Mechanism cannon when the creaking and groaning emanating from the laminated timber weapon had him in fear of his life and he quickly abandoned any plans to shoot one monster with another.

Note that heavy side plate trigger mechanisms are for ballasting purposes in extra heavy duty or "Main Battle Tank" underwater weapons.
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Old 10-28-2018, 06:02 PM   #126
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Re: Trigger Mechanism Design Rules

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In the interests of Science I have ordered an Ermes-Sub Double Roller mech and plan to "put it to the test". Planet Multi Store, whom I have dealt with before, have a special price offer at the moment on this product.

https://www.planetdivestore.com/dive...25941/84478/sc
The Ermes-Sub Double Roller mech arrived yesterday and now I can finally see what had been hidden from view in previous threads on this mechanism. These Ermes-Sub reverse trigger mechanisms are not “dry fire” mechanisms, although if you pull the trigger on an upright mechanism on its own then the sear lever falls due to its weight. More later once I figure out how to remove the pivot pins which appear to have peened over ends, no doubt to prevent them falling out, or being pushed out. The sear “tooth” roller is a bit smaller OD than I thought it would be, but the pivot pin spacing is good.

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Old 11-25-2018, 07:17 PM   #127
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Re: Trigger Mechanism Design Rules

An old email which may be of interest here.

I spoke with Wally Gibbins many years ago and asked him about his
trigger mechanism design and the mechanisms that were contemporaneous
with it, both at the time and before. Wal actually documented it all
later in a personal letter to me which I later had published
posthumously by Wal thanks to Barry Andrewartha of IF&SN so that Wal
could speak directly to the “brotherhood” and in a sense, in his
farewell salutation, “sign off” for a last and final time. In the old
days they would have regarded an Omer “Cayman” as a childlike weapon
no better than a toy, being of a flimsy construction that would not
last a week, much less a season. Of course that would be judging it
by the plastic guns of the time, the feeble and simplistic
holidaymaker's guns from the Europeans that shot fork head tridents on
top of skinny shafts and were a low cost option to their more serious
weapons such as the legendary “Champion Arbalete” with its socket
head muzzle, preferably the version with four sockets. A gun was
expected to use either 5/8” or 3/4” solid bands of gum rubber and
either a 5/16” or 3/8” diameter shaft just in case any sharks had to
be seen off with a shot driven through them.

The square notch spear tail is a direct carry lover from the
single-piece trigger, as any significant angle on the tooth and the
mechanism shoots without you pulling the trigger. The angled sear
tooth used by the Europeans is a direct carry over from the pull down
sear, spring gun mechanism, as with a square cut tooth pulling the
trigger would otherwise drive the shaft back against the spring
loading/band pull. Once cam lock mechanisms were created they were
two state, i.e. either cocked or discharged, and why divers like them
is that they can be “dry fired” to check the latch and release action
on the spear without any band load. As timber guns of any reasonable
length (in excess of a metre) are going to have some depth to the
stock, the “real estate”already being there it makes sense to fill it
up with the mechanism. A sear box is not only held in with the
transverse pins, its forward edge presses hard on the stock, hence a
deep mechanism case transfers its load into the stock by butting
squarely into the pocket cut for it in the timber. You can see this
very clearly in the Riffe Metaltech as the sear case in its plastic
isolation cradle butts directly to the stock.

The reason why Wally Gibbins made his reverse mechanism, seen in the
“Sea Hornet” and “Biller” in somewhat economy versions, is that he
wanted that two state mechanism with a distinct “cock” and “release”,
in fact the spear could cock the mechanism with a “slight push on it
with one finger” was a familiar phrase used by Wal. I have used that
trigger mechanism, in its all metal case configuration, ever since I
started diving nearly fifty years ago, with the Undersee mechanism
being used in my long range cannons until I replaced the sear pin
“rivet” with something more substantial, just as Jay Riffe did with
his own version of the Undersee which is fully made from stainless
steel.
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Old 12-19-2018, 08:47 PM   #128
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Re: Trigger Mechanism Design Rules

Some history which I recovered from an old computer hard disk. Here is the model in clear plastic which Mori created that eventually became the Kitto M6 through to the M8 multi-lever trigger mechanism, now used for some years in the latest JBL timber (woody) spearguns. At the time Mori was working on a mechanism cassette/sear box housing and figuring out the auto-line release action in terms of which lever to drive it off.

When I first saw Mori's model I was concerned that it was a hooking mechanism and not a cam lock as the locking lever does not roll into the trigger, instead they are one and the same thing. However time has proven that it was not going to be a problem provided all the levers are fully engaged when locked.

At the time I was working on a four pivot pin, two stage mech, but thought the close set and "lean on each other" levers could be used in a four lever mech using the general shapes of Mori's levers. The parts ended up being too small and the demands on precision were great, so this "fourpin" mech never got beyond some plastic models to check it out, aided by the addition of “timing bumps” on the levers to “short circuit” the cocking or relatch action.
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Old 02-23-2019, 05:49 PM   #129
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Re: Trigger Mechanism Design Rules

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Wally Potts followed Jack Prodanovich's lead in using the "balanced sear" design in his own later model spearguns. The "balanced sear" lever design, developed by Prodanovich using his genius for innovating and perfecting spearfishing equipment, allows a pivot position for the sear lever which is essentially the same one as would be used for a single-piece trigger. Such an arrangement would not usually allow the sear tooth to roll forwards under band pull action from the shaft tail as its function is to hold the shaft until the trigger is pulled by the operator. What causes it to roll here (the Wally Potts diagram is attached) is that the sear lever is destabilized by cutting an angled sear tooth with a matching angle cut into the spear tail notch. Through patient experimentation Prodanovich had varied the tooth angles and the fore-aft offsets of the tooth position from the sear pivot pin and thus discovered that the sear lever could transition from hanging up, as is required in a single-piece trigger, to just turning with the load, but at a minimum level of torque. Thus he could control trigger pull in his trigger mechanism to be low even with very high band loads, despite no significant gearing in the sear lever component and a close spacing of the pivot pins in the mechanism housing which usually limits the gearing. Thus Prodanovich had beaten two of the trigger mechanism design rules at one stroke. His mechanisms were either set up for high power use, he had tested it for 800 pounds band load and had one in his big Tuna gun (at 1,000 pounds!) which threw a heavy shaft with a tandem lapped band layout. Like a gas operation pistol the speargun functioned best with "high power ammunition", but for lower band loads the mechanism was tuned to offer more torque at those reduced force levels to roll the sear lever. An impressive feat for a self-taught engineer and one not recognized by many who know of his pioneering development work.

The Potts version of this mechanism has been designed for 400 pounds band load and uses a sear tooth angle that suits this mechanism's particular geometry which is very different to that found in the Prodanovich gun. The diagram shown here is basically an installation instruction sheet and provides the method to dismantle it for inspection, it is not an engineering drawing, but shows the general internal layout.

http://rocknfish.com/Jack%27s_Tuna_Gun.html
The rocknfish website is no longer up, so here is Jack's Tuna Gun on display at James and Joseph, San Diego. Wally Potts timber gun is below it.

KABOOM spearfishing at maximum power!
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Old 03-26-2019, 11:15 PM   #130
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Re: Trigger Mechanism Design Rules

The double roller trigger mechanism is designed for a smooth release by eliminating “stump jumping” off the sear tooth as spear tails pop free of the reverse trigger mechanisms, however there is a simpler fix by extending forwards the sear box roof on these now rather open mouth reverse trigger mechanisms. To accommodate an increased wishbone draw the forward sear box roof extension can be slotted to allow spear tails to be driven from further rearwards by accepting the insertion of the shark fin tab. To illustrate this point I show a mechanism modified accordingly. I originally designed this top slotted mechanism for Doug Battersby, but he never got around to using it. The top slot also functions as an anti-shaft rotation or rolling device. (Doug Battersby was a member of the Rollergun Group that included myself, John Warren, Nikko Brummer (founder), Memo and Franceso, but my memory fails me on the others, although the group was always small in number, but big in ability, knowledge and spearfishing experience).

The concept of a slotted sear box case belongs to Australian spearfishing great Wally Gibbins, only in his case the shaft tail tab was on one side (the right) and so was the slot. This system was used on his very early Carbine style shoulder gun and a similar slot was in the muzzle hoop to allow the side lug to escape which was also the shooting line attachment to the shaft. Australians in the early days needed powerful guns to take care of sharks, of which there were plenty, but "thanks" to the actions of the green movement those numbers, which had been whittled down ruthlessly in the past, have been allowed to grow alarmingly again.

European guns in the early days, and that included spring guns of 2 meters, lacked the sheer grunt to transfix a shark that needed to be seen off quickly, and hence the desirability of 3/8" diameters shafts in Australian waters and the guns with the necessary pep to propel them. Wally's shoulder gun used racecourse starting gate rubber for twin 3/4" bands, so that delivered the necessary horsepower.
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Old 03-27-2019, 06:17 AM   #131
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Re: Trigger Mechanism Design Rules

As a matter of interest here is a sketch from Wally showing the side-slotted sear box and rear tabbed shaft. Note that this is prior to the use of line slides and is an advancement on tying shooting lines to just behind the spear tip as was done previously. In the lower sketch you can see the two band muzzle and the side slotted muzzle hoop that let the shaft tail tab through which carried the shooting line. The spear was fabricated from stainless steel with the shark fin-like tail lug welded on and is a slice of spearfishing history that would otherwise have been forgotten.

The historic photo shows Wal after having bagged a big one with his trusty shoulder gun which was constructed with all home-made parts in that nothing used in it came from mass production speargun parts, the gun in its earlier versions predating all modern band spearguns.
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Last edited by popgun pete; 04-03-2019 at 02:13 PM. Reason: Added a photo of a couple of Wal's guns on display some years ago
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Old 04-02-2019, 06:59 PM   #132
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Re: Trigger Mechanism Design Rules

The Seatec eurogun has been around for some years now and has a very unusual trigger mechanism in that it has three elements; a sear lever, an idler wheel and a trigger each with their own pivot pin. At first glance this type of gun would be expected to use a cam lock trigger mechanism, but here Seatec have turned the arrangement into a hooking mechanism. That could have been a disaster as hooking mechanisms don't actually cam lock being more like a geared single piece trigger. In this mechanism the idler wheel reverses the push direction on the trigger, instead of compressing the trigger it tries to stretch it which is not a great idea. The idler wheel has no reduction gearing as the force in and force out radial lengths are much the same. Despite being a long mechanism the locking circle is rather small as the circle is set by the idler wheel to trigger pivot pin spacing. What saves this mechanism is the hooking contact and trigger pivot force action line run slam bang right on the periphery of the intermediate circle (shown in green) and the long trigger provides a lot of leverage. It could be argued that the layout gives a very long trigger and there is the usual gearing in the sear lever and the resultant humpy back grip housing is reasonably attractive.

Hooking trigger mechanisms need a good safety and in this trigger mechanism a sliding block moves in from the rear and catches on the back of the trigger. For the trigger to override the safety it would have to break the plastic block that is moved forwards by an external slide button. On this type of trigger mechanism you need to make sure that you use it as it also pushes the trigger closed and makes sure that it is hooking the idler wheel as otherwise the safety seems to jam and not slide. Remove this safety at your peril!
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Old 04-02-2019, 11:01 PM   #133
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Re: Trigger Mechanism Design Rules

Where an idler wheel or reversing lever would be useful is for the lower trigger mechanism in a twin spear "over and under" speargun. I have just hacked around the “Seatec” mechanism to give a rough idea of how such an “upside down” mechanism would look. There is a problem with the biasing springs if only one is to be used in addition to the torsion spring already on the idler wheel, however a compression spring behind the trigger would be one solution as it could be installed in the handgrip body similar to the trigger spring used in a JBL "Magnum" trigger mechanism. The advantage of using the center lever is the resultant trigger mechanism is of the cam lock type whereas most such guns use a hooking mechanism.
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Old 04-03-2019, 02:10 AM   #134
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Re: Trigger Mechanism Design Rules

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The Seatec eurogun has been around for some years now and has a very unusual trigger mechanism in that it has three elements; a sear lever, an idler wheel and a trigger each with their own pivot pin. At first glance this type of gun would be expected to use a cam lock trigger mechanism, but here Seatec have turned the arrangement into a hooking mechanism. That could have been a disaster as hooking mechanisms don't actually cam lock being more like a geared single piece trigger. In this mechanism the idler wheel reverses the push direction on the trigger, instead of compressing the trigger it tries to stretch it which is not a great idea. The idler wheel has no reduction gearing as the force in and force out radial lengths are much the same. Despite being a long mechanism the locking circle is rather small as the circle is set by the idler wheel to trigger pivot pin spacing. What saves this mechanism is the hooking contact and trigger pivot force action line run slam bang right on the periphery of the intermediate circle (shown in green) and the long trigger provides a lot of leverage. It could be argued that the layout gives a very long trigger and there is the usual gearing in the sear lever and the resultant humpy back grip housing is reasonably attractive.



Hooking trigger mechanisms need a good safety and in this trigger mechanism a sliding block moves in from the rear and catches on the back of the trigger. For the trigger to override the safety it would have to break the plastic block that is moved forwards by an external slide button. On this type of trigger mechanism you need to make sure that you use it as it also pushes the trigger closed and makes sure that it is hooking the idler wheel as otherwise the safety seems to jam and not slide. Remove this safety at your peril!


Great to see you discussing this trigger here. I was planning on doing that myself but you did a better job than I would have done.

It took me some time of head scratching to understand why exactly it feels so smooth. Eventually I realized that the length and lever of the trigger caused the smooth release.

It was designed by Valerio Grassi who worked as a gun and rifle designer for Baretta.

My Seatec Snake speargun that’s using this trigger is only a 65. I wonder if the larger guns where more force is applied on the trigger shoot just as well?

In CMAS target shooting competitions it’s mandatory to use commercially available spearguns. Custom guns are not allowed I believe. The Seatec Snake is often seen in competition because of its great accuracy.
I have the same experience and the range and accuracy of my little 65 is incredible. I believe the trigger contributes to that.
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Old 04-03-2019, 02:42 AM   #135
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Re: Trigger Mechanism Design Rules

The trigger arm leverage can be assessed by looking at the length of the red line from the trigger pivot pin to the release notch on the idler wheel and the length of the orange line from the trigger pivot pin to the place where your finger pulls-on the trigger. In the attached diagram I have added the circles at these two radii in red and orange respectively. The trigger does not have far to swing at the retention notch, but the trigger tip swings circumferentially further being at a greater radius from the pivot pin.

There are two versions of this trigger, the gold handle as shown with all metal parts and a silver version with plastic parts for the idler wheel and trigger.
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